Combustion chamber structure for an internal combustion engine

ABSTRACT

To accelerate a combustion with an entire combustion chamber including the vicinity of an opening portion for air suction to thereby make uniform a flame propagation in a combustion chamber structure for an internal combustion engine, and to provide a technology for preventing the generation of knocks, a longitudinal sectional shape of a top wall surface of the combustion chamber is in the form of a substantially triangular shape in longitudinal section defined and surrounded by a cylinder head, a cylinder and a piston. A projection is provided on a circumferential edge portion of a top surface of the piston, with a surface, facing the top wall surface of the combustion chamber, of the projection being substantially in parallel with the top wall surface of the combustion chamber. A cutaway portion is formed in the vicinity of at least a portion, facing the intake opening portion, of the projection of the top surface of the piston.

BACKGROUND OF THE INVENTION

The present invention relates to a combustion chamber of an internalcombustion engine.

A combustion chamber structure of an internal combustion engine is knownto improve a combustion rate of mixture in the internal combustionengine as shown in, for example, Japanese Utility Model ApplicationLaid-Open No. SHO 60-102428.

The combustion chamber structure of the internal combustion engine is asfollows. A circumferential edge portion of a top of a piston and acircumferential edge portion of an inner wall of a cylinder head areprojected with each other so that, when the piston is located in thevicinity of the top dead center, the circumferential edge portion of thetop of the piston and the circumferential edge portion of the inner wallof the cylinder head are close to each other to form a squish area forgenerating a so-called squish flow.

Then, in the combustion chamber, a spark plug is disposed in the innerwall surface of the cylinder head more on the exhaust valve side thanthe position where the squish flow collides, directed to the center ofthe combustion chamber from the squish area.

With such a structure of the combustion chamber of the internalcombustion chamber, in a final stage of a compression stroke, thecircumferential edge portion of the inner wall surface of the cylinderhead and the circumferential edge portion of the top of the piston areclose to each other so that the squish area is narrowed. Accordingly,air or mixture located in the squish area is directed to the centralportion of the combustion chamber in the form of the squish flow.

The squish flows directed to the central portion of the combustionchamber collide with each other to generate a turbulence. By thisturbulence, the combustion of the central portion of the combustionchamber is accelerated.

Next, when the internal combustion takes an expansion stroke from thecompression stroke and the piston starts to be lowered, the squish areais expanded, a phenomenon which is referred to as a reverse squish inwhich the mixture is sucked in the expanded squish area is generated.When the mixture is sucked into the squish area by the reverse squish, aflame generated by the spark plug also reaches the vicinity of thesquish area from the central portion of the combustion chamber by theabovedescribed reverse squish. Then, when the squish area is expanded inaccordance with the further lowering movement of the piston, theabove-described flame is sucked into the squish area to thereby burn themixture within the squish area.

The above-described combustion chamber structure of the internalcombustion engine is thus used for accelerating the combustion of theportion where the flame propagation is slow, thereby making uniform theflame propagation, i.e., for reducing the difference in the combustioncompletion timing at each circumferential portion.

By the way, an intake opening portion for introducing new air andmixture into the combustion chamber and an intake valve foropening/closing the intake opening portion are provided in the cylinderhead. Thus, since a temperature of the vicinity of the intake openingportion is lowered by the introduction of the cold new air and mixture,it is necessary to accelerate the combustion in this portion.

However, since it is necessary to provide a clearance to some extent inorder to avoid the contact between the intake valves and the piston topsurface, in between the vicinity of the intake opening portion and thepiston top surface, it is impossible to form the squish area of thesuitable clearance and it is difficult to accelerate the combustion inthe vicinity of the intake opening portion. As a result, there is a fearthat the mixture residing in the vicinity of the intake opening portionis self-ignited before the flame generated by the ignition of the sparkplug has reached the place, resulting in a knock of the combustion.

SUMMARY OF THE INVENTION

In view of the above-described defects, the present invention has beenmade, and therefore has an object of the present invention to provide atechnology to prevent generation of a knock of combustion while makingthe flame propagation uniform by accelerating the combustion in theportion where the flame propagation is slow as in the vicinity of theintake opening portion.

In order to solve the above-noted defects, the following means isadopted according to the present invention.

A combustion chamber structure for an internal combustion engineaccording to the present invention, a longitudinal sectional shape of atop wall surface of a combustion chamber is in the form of asubstantially triangular shape in longitudinal section in one directionpassing through a center of the combustion chamber defined andsurrounded by a cylinder head, a cylinder and a piston, with a sparkplug being disposed at an apex portion of the triangular shape and anintake opening portion and an exhaust opening portion on the top surfaceof the combustion chamber, and is characterized in that:

a projection is provided on a circumferential edge portion of a topsurface of the piston, with a surface, facing the top wall surface ofthe combustion chamber, of the projection being substantially inparallel with the top wall surface of the combustion chamber; and

a cutaway portion is formed in the vicinity of at least a portion,facing the intake opening portion, of the projection of the top surfaceof the piston.

In this combustion chamber structure of the internal combustion engine,when the internal combustion chamber takes a shift in latter half of thecompression stroke, the piston is raised up to the vicinity of the topdead center, the projection of the top surface of the piston and the topwall surface of the combustion chamber are close to each other to form asquish area. Then, when the piston is further raised, the squish area isnarrowed so that the air, the mixture and the like that are residual inthe squish area are advanced toward the central portion of thecombustion chamber in the form of squish flows.

In this case, since the surface, facing the top wall surface of thecombustion chamber, of the projection of the top surface of the pistonis formed substantially in parallel with the top wall surface of thecombustion chamber, the squish flows are advanced substantially inparallel with the top wall surface of the combustion chamber to flowtoward the apex portion of the combustion chamber, i.e., the vicinity ofthe spark plug. Then, the squish flows that have been advanced close tothe spark plug are brought into collision with each other to form theturbulence in the vicinity of the spark plug so that the combustion inthe vicinity of the spark plug is accelerated.

Also, the air and mixture located in the squish area in the vicinity ofthe cutaway portion is introduced into the cutaway portion and collidewith each other to generate the turbulence.

Then, when the internal combustion engine takes a shift from thecompression stroke to the expansion stroke, and the piston starts to belowered, the squish area is expanded so that the reverse squish flowsare generated toward the squish area from the central portion of thecombustion chamber. The reverse squish flows are advanced substantiallyin parallel with the top wall surface of the combustion chamber.

According to the present invention, since the surface, facing the topwall surface of the combustion chamber, of the projection of the topsurface of the piston is formed substantially in parallel with the topwall surface of the combustion chamber, the reverse squish flows arestrongly sucked into the squish area.

The reverse squish flows that have been sucked in the squish area reachthe cylinder wall surface within the squish area and change theirdirections at the reached cylinder wall surface to advance in thecircumferential direction along the wall surface of the cylinder.

The reverse squish flows that have changed the directions in the squisharea around the cutaway portion are introduced into the cutaway portionsand collided with each other to generate the turbulence. The turbulencebecomes strong together with the turbulence generated in the previouscompression stroke to accelerate the mixture residing around the cutawayportion, i.e., the mixture residing in the vicinity of the intakeopening portion to thereby make uniform the flame propagation in thecombustion chamber.

Accordingly, the mixture located in the vicinity of the intake openingportion where it is said that the flame propagation is slowest is burntbefore the self-ignition to thereby suppress the generation of knocks.

Incidentally, the cutaway portion according to the present invention,formed in the vicinity of the portion facing the intake opening portion,may serve also as a valve recess in the projection of the top surface ofthe piston for avoiding any contact between the intake valve foropening/closing the intake opening portion and the piston.

Subsequently, in the case where the internal combustion engine isprovided with a swirl flow generating means for generating swirl flowswithin the combustion chamber, the cutaway portion may be constructed bya groove formed in a direction in which the swirl flows generated by theswirl flow generating means are received so that the swirl flows areintroduced into the cutaway portion, or the cutaway portion may beconstructed by a groove formed in a direction in which the swirl flowsgenerated by the swirl flow generating means are not received so thatthe swirl flows are not introduced into the cutaway portion.

Also, in the case where the internal combustion engine is provided witha tumble flow generating means for generating vertical eddy flows(tumble flows) within the combustion chamber, the cutaway portion may beconstructed by a groove formed in a direction in which the tumble flowsgenerated by the tumble flow generating means are received so that thetumble flows are introduced into the cutaway portion, or the cutawayportion may be constructed by a groove formed in a direction in whichthe tumble flows generated by the tumble flow generating means are notreceived so that the tumble flows are not introduced into the cutawayportion.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a cross-sectional view showing a combustion chamber structurein accordance with a first embodiment of the invention;

FIG. 2 is a plan view showing the structure of an inner wall surface ofa cylinder head;

FIG. 3 is a plan view showing the structure of a piston;

FIG. 4 is a view (1) illustrating a flow direction of squish flows;

FIG. 5 is a view (2) illustrating a flow direction of the squish flows;

FIG. 6 is a view (1) illustrating a flow direction of reverse squishflows;

FIG. 7 is a view (2) illustrating a flow direction of the reverse squishflows;

FIG. 8 is a view (1) showing another example of cutaway portions inaccordance with the first embodiment;

FIG. 9 is a view (2) showing the example of the cutaway portions inaccordance with the first embodiment;

FIG. 10 is a cross-sectional view showing the structure of a combustionchamber in accordance with a second embodiment;

FIG. 11 is a plan view showing the structure of an inner wall surface ofa cylinder head;

FIG. 12 is a plan view showing the structure of a piston;

FIG. 13 is a view showing another example of cutaway portions inaccordance with the second embodiment;

FIG. 14 is a cross-sectional view showing the structure of a combustionchamber in accordance with a third embodiment;

FIG. 15 is a plan view showing the structure of a piston; and

FIG. 16 is a view showing another example of cutaway portions inaccordance with the third embodiment;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure of a combustion of an internal combustion engine accordingto the present invention will now be described with reference to theaccompanying drawings.

Embodiment 1.

FIG. 1 is a view showing the structure of a combustion chamber of aninternal combustion engine according to a first embodiment of theinvention.

A combustion chamber 1 is defined by an inner wall surface 20 of acylinder head 2, a wall surface 30 of a cylinder formed in a cylinderblock 3, and a top surface of a piston 4 installed slidably within acylinder.

The inner wall surface 20 of the cylinder head 2 forms a top wallsurface of the combustion chamber 1 and is shaped substanitally into asubstantially triangle in longitudinal sectioning one direction, i.e., aso-called pent-roof. A spark plug 5 is disposed at an apex portion ofthe inner wall 20. As shown in FIG. 2, two opening portions 7 for airsuction are provided on one side and two opening portions 8 for airexhaustion are provided on the other side around the spark plug 5.Projecting portions 6 are formed on a circumferential edge portion ofthe inner wall surface 20 except for the opening portions 7 and 8.

Turning back to FIG. 1, a projection 40 is formed also in thecircumferential portion of the top surface of the piston 4. For thisreason, a recess portion surrounded by the projection 40 is formed inthe top surface of the piston 4. Then, a lower surface of the projectingportions 6 and a top surface of the projection 40 which are located toface each other are formed substantially in parallel with the inner wallsurface 20 of the cylinder head 2. When the internal combustion enginetakes the final stage of the compression stroke, the lower surface ofthe projecting portions 6 and the upper surface of the projection 40 areclose to each other in accordance with the raising movement of thepiston 4 to form the squish area 9 extending in a skew direction.

Furthermore, as shown in FIG. 3, a plurality of cutaway portions 10 areformed in the projection 40 of the piston 4. The cutaway portions 10 areformed for generating a turbulence for entraining the air and themixture of the squish areas 9, located on both adjacent sides of eachcutaway portion 10, and collidating the entrained air and mixture whenthe piston is raised in the vicinity of the top dead center of thecombustion. Then, a depth of the cutaway portions 10 is increased towardthe inner circumferential side from the outer circumferential side ofthe piston 4 so that a stronger turbulence is generated on the innercircumferential side than the outer circumferential side. With respectto the positions of the above-described cutaway portions 10, the cutawayportions are provided at least at portions facing the opening portion 7for air suction where the flame propogation is slowest and a knock aliable to be generated.

The operation and effect of the combustion chamber structure of theinternal combustion engine according to this embodiment will now bedescribed.

First of all, when the piston 4 is raised to the vicinity of the topdead center in latter half of the compression stroke of the internalcombustion engine, as shown in FIG. 4, the projecting portions 6 of thecylinder head 2 and the projection 40 of the piston 4 are close to eachother to thereby form the squish areas 9. Then, when the piston 4 isfurther raised, the squish areas 9 are narrowed so that the squish flowsS are generated in which the air and mixture within the squish area 9are directed from the circumference of the internal combustion chamber 1toward the vicinity of the spark plug 5.

The above-described squish flows S are advanced substantially inparallel with the inner wall surface 20 of the cylinder head 2 along theupper surface of the projection 40 and the lower surface of theprojecting portions 6. Accordingly, the squish flows S are caused toflow toward the spark plug 5 without any attenuation caused by thecontact of the inner wall surface 20 of the cylinder head 2 or the like.

The squish flows S that flow from the circumference of the combustionchamber 1 to the vicinity of the spark plug 5 are collided with eachother in the vicinity of the spark plug 5 to generate the turbulence.

Also, out of the air and the mixture located in the squish areas 9, theair and mixture located in the squish area 9 in the vicinity of thecutaway portions 10 of the above-described piston 4 are caused to flowinto the cutaway portions 10 in accordance with the elevating movementof the piston 4. For example, as shown in FIG. 5, the air and mixture ofthe squish areas 9, located on both adjacent sides of each cutawayportion 10 are caused to flow into the cutaway portion 10 while becominga flow t1 from one squish area 9 and a flow t2 from the other squisharea. These flows t1 and t2 are collided with each other in the cutawayportion 10 to generate the turbulence.

Subsequently, when the peak plug 5 is ignited, the combustion in thevicinity of the spark plug 5 is accelerated by the turbulence generatedby the collision of the above-described squish flows S.

Then, when the internal combustion engine takes the sift shift from thecombustion stroke to the expansion stroke so that the piston 4 starts tobe lowered, the reverse squish in which the mixture is sucked into thesquish areas 9, is generated. As shown in FIG. 6, by the reverse squish,the mixture forms a flow R that advances radially outwardly along theinner wall surface 20 of the cylinder head 2 from the central portion ofthe combustion chamber 1. At this time, the lower surface of theprojecting portion 6 and the top surface of the projection 40 formingthe squish areas 9 are formed substantially in parallel with the innerwall surface 20 of the cylinder head 2 and the step between theprojecting portions 6 and the inner wall surface 20 of the cylinder head2 is relatively small. Accordingly, the flows R would not be attenuatedby the collision with the step and would be sucked into the squish areas9 with a large power to reach the cylinder wall surface 30.

Thereafter, the flame produced by the ignition of the spark plug 5 isalso advanced close to the squish area 9 by the flows R, and is suckedwithin the squish area 9 in accordance with the further downwardmovement of the piston 4 to well reach the wall surface 30 of thecylinder. Thus, the mixture that has been sucked within the squish area9 is rapidly burnt.

Furthermore, as shown in FIG. 7, the flows R that have reached the wallsurface 30 of the cylinder are brought into contact with the wallsurface 30 of the cylinder to change their directions and to becomeflows R′ which are directed in the circumferential direction along thewall surface 30 of the cylinder. At this time, the flows R′ which havebeen formed in the squish area 9 in the vicinity of the above-describedcutaway portions 10 are introduced into the cutaway portions 10. Theflows R′ are in collision with each other to form the turbulence. Theturbulence becomes stronger together with the turbulence generated inthe previous compression stroke to accelerate the combustion in thevicinity of the abovedescribed cutaway portions 10. As a result, thecombustion in the vicinity of the intake opening portions 7 for airsuction where it is said that the flame propagation is slowest isaccelerated and effected before the mixture in the vicinity of theopening portions 7 for air suction is self-ignited.

Accordingly, in the combustion chamber structure of the internalcombustion engine in accordance with this embodiment, the squish area 9that is substantially in parallel with the inner circumferential wallsurface 20 of the cylinder head is formed so that the flame stronglyreaches the wall surface 30 of the cylinder to accelerate the combustionin the vicinity of the cylinder wall surface 30. Furthermore, themixture and the flame that have strongly reached the cylinder wallsurface 30 are introduced into the cutaway portions 10 to be incollision with each other within the cutaway portions 10 to generate theturbulence. It is therefore possible to accelerate the combustion in thevicinity of the opening portions 7 for air suction where it would bedifficult to form a sufficient squish area. As a result, the flamepropagation is made uniform within the combustion chamber 1 to preventthe generation of knocks.

Incidentally, as shown in FIGS. 8 and 9, the cutaway portions may alsoserves serve as valve recesses for avoiding the collision between thepiston 4 and the intake valves (not shown) for opening/closing theopening portion 7 for air suction.

Embodiment 2.

An example in which the combustion chamber structure of the internalcombustion engine in accordance with the present invention is applied toa lean combustion type internal combustion engine will now be describedwith reference to FIGS. 10 to 12. In this case, the explanation thereforwill be given only to the structure that is different from that of theforegoing first embodiment. The explanation of the like structure willbe omitted.

In FIGS. 10 and 11, a straight port 17 having a straight flow path isconnected to one of two opening portions 7 for air suction formed in thecylinder head 2, whereas a swirl port 11 having a flow path in thetangential direction of the combustion chamber 1 is connected to theother opening portion 7 for air suction.

Then, a swirl control valve SCV for opening/closing the flow path of thestraight port 17 is provided in the straight port 17. When the swirlcontrol valve SCV is closed, the new air is introduced into thecombustion chamber 1 only from the swirl port 11 so that the introducednew air forms the swirl flows SW.

Thus, the swirl port 11 and the swirl control valve SCV realizes theswirl generation means according to the present invention.

Subsequently, as shown in FIG. 12, the cutaway portions 12 constructedby the grooves formed in the direction in which the swirl flows SW arereceived, are formed in a projection 40 formed in the circumferentialedge portion of the top surface of the piston 4, so that a part of theswirl flows SW is introduced into the cutaway portions 12. The cutawayportions 12 are formed in the portion of the top surface of the piston 4which faces the opening portions 7 for air suction in the same manner asin the first embodiment.

The other structure is the same as that of the first embodiment.

The operation and effect of this embodiment will now be described.

First of all, when in the compression stroke of the internal combustionengine, the swirl control valve SCV is closed and at the same time, theintake valves (not shown) open the opening portions 7 for air suction,the new air is introduced into the combustion chamber 1 only from theswirl port 11 to thereby form the swirl flows SW. Then, when the pistonis raised to the top dead center in latter half of the compressionstroke, a part of the swirl flows SW is introduced into the cutawayportions 12, and the air and mixture are introduced from the squish area9 in the vicinity of the cutaway portions 12 so that these flows are incollision with each other to produce the turbulence.

Subsequently, when the internal combustion engine takes the shift fromthe compression stroke to the expansion stroke so that the piston 4starts to be lowered, the reverse squish in which the mixture is suckedinto the squish areas 9, is generated. By the reverse squish flows, themixture is advanced from the central portion of the combustion chamber 1radially outwardly along the inner circumferential wall surface 20 ofthe cylinder head 2, and is sucked strongly into the squish area 9.Then, the mixture that has been sucked into the squish are area 9strongly reaches the cylinder wall surface 30.

Thereafter, the flame produced by the ignition of the spark plug 5 isalso advanced to the vicinity of the squish area 9 in the same manner asthe mixture, and is strongly sucked into the squish area 9 in accordancewith the downward movement of the piston 4 to strongly reach the wallsurface 30 of the cylinder. Thus, the mixture that has been sucked intothe squish area 9 is rapidly burnt.

Furthermore, the flows of the mixture and flame that have reached thewall surface 30 of the cylinder are brought into contact with the wallsurface 30 of the cylinder to change their directions and to be directedin the circumferential direction along the wall surface 30 of thecylinder. Then, the flows of the mixture are introduced into the cutawayportions 12 to form the stronger turbulence together with the turbulencegenerated in the previous compression stroke. As a result, thecombustion in the vicinity of the opening portions 7 for air suctionwhere the flame propagation is slowest is accelerated and effectedbefore the mixture in the vicinity of the opening portions 7 for airsuction is self-ignited.

Incidentally, as shown in FIG. 13, it is possible to change the shape ofthe cutaway portions of the piston 4 to the grooves 13 formed in adirection where the swirl flows are not received. In this case, sincethe swirl flows are not introduced into the cutaway portions 13, it ispossible to obtain the same advantage as that of the first embodimentwithout attenuating the swirl flows.

Embodiment 3.

An example in which the combustion chamber structure of the internalcombustion engine in accordance with the present invention is applied toa lean combustion type internal combustion engine in which a verticaleddy flows (tumble flows) will now be described with reference to FIGS.14 to 16. In this case, the explanation therefor will be given only tothe structure that is different from that of the foregoing firstembodiment. The explanation of the like structure will be omitted.

In FIG. 14, a tumble port 14 for producing vertical eddy flows withinthe combustion chamber 1 is connected to two opening portions 7 for airsuction formed in the cylinder head 2 of the lean combustion typeinternal combustion engine.

Subsequently, as shown in FIG. 15, the cutaway portions 15 constructedby the grooves formed in a direction where the above-described tumbleflows are received, are formed in a projection 40 formed on thecircumferential edge portion of the top surface of the piston 4 so thata part of the tumble flows is introduced into the cutaway portions 15.The cutaway portions 15 are formed in the portion of the top surface ofthe piston 4 which faces the opening portions 7 for air suction in thesame manner as in the first embodiment.

The other structure is the same as that of the first embodiment.

The operation and effect of this embodiment will now be described.

First of all, when in the compression stroke of the internal combustionengine, the intake valves (not shown) open the opening portions 7 forair suction, the new air is introduced into the combustion chamber 1only from the tumble port 14 to thereby form the tumble flows. Then,when the piston is raised to the top dead center in latter half of thecompression stroke, a part of the tumble flows is introduced into thecutaway portions 15, and the air and mixture are introduced from thesquish area 9 in the vicinity of the cutaway portions 15 so that thesefollows are in collision with each other to produce the turbulence.

Subsequently, when the internal combustion engine takes the shift fromthe compression stroke to the combustion stroke so that the piston 4starts to be lowered, the reverse squish in which the mixture is suckedinto the squish areas 9, is generated. By the reverse squish flows, themixture is advanced from the central portion of the combustion chamber 1radially outwardly along the inner circumferential wall surface 20 ofthe cylinder head 2 and is sucked strongly into the squish area 9. Then,the mixture that has been sucked into the squish are area 9 stronglyreaches the cylinder wall surface 30.

Subsequently, the flame produced by the ignition of the spark plug 5 isalso advanced to the vicinity of the squish area in the same manner asthe mixture, and is strongly sucked into the squish area 9 in accordancewith the downward movement of the piston 4 to strongly reach the wallsurface 30 of the cylinder. Then, the mixture that has been sucked intothe squish area 9 is rapidly burnt.

Furthermore, the flows of the mixture and flame that have reached thewall surface 30 of the cylinder are brought into contact with the wallsurface 30 of the cylinder to change their directions and to be directedin the circumferential direction along the wall surface 30 of thecylinder. Then, the flows of the mixture are introduced into the cutawayportions 15 to form the stronger turbulence together with the turbulencegenerated in the previous compression stroke. As a result, thecombustion in the vicinity of the opening portions 7 for air suctionwhere it is said that the flame propagation is slowest is acceleratedand effected before the mixture in the vicinity of the opening portions7 for air suction is self-ignited.

Incidentally, as shown in FIG. 16, it is possible to change the shape ofthe cutaway portions of the piston 4 to the grooves 16 formed in adirection where the tumble flows are not received. In this case, sincethe tumble flows are not introduced into the cutaway portions 16, it ispossible to obtain the same advantage as that of the first embodimentwithout attenuating the tumble flows.

Various details of the invention may be changed without departing fromits spirit not its scope. Furthermore, the foregoing description of theembodiments according to the present invention is provided for thepurpose of illustration only, and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

What is claimed is:
 1. A combustion chamber structure for an internalcombustion engine, in which a longitudinal sectional shape of a top wallsurface of a combustion chamber is in the form of a substantiallytriangular shape in longitudinal section in one direction passingthrough a center of the combustion chamber defined and surrounded by acylinder head, a cylinder and a piston, with a spark plug being disposedat an apex portion of the triangular shape and an intake opening portionand an exhaust opening portion on the top surface of the combustionchamber, wherein: a projection is provided on a circumferential edgeportion of a top surface of the piston, with a surface, facing the topwall surface of the combustion chamber, of said projection beingsubstantially in parallel with the top wall surface of the combustionchamber; and a cutaway portion is formed in the vicinity of at least apiston wholly formed within a portion , facing the intake openingportion, of said the projection that faces an intake opening of the topwall surface area of the piston combustion chamber.
 2. The combustionchamber structure according to claim 1, wherein an intake valve isprovided to be openable/closeable in the opening portion for airsuction, and said cutaway portion serves also as a valve recess foravoiding any contact between the intake valve and the piston when theintake valve is projected into the combustion chamber.
 3. The combustionchamber structure according to claim 1, further comprising a swirl flowgenerating means for generating swirl flows within the combustionchamber, wherein said cutaway portion is constructed by a groove formedin a direction in which the swirl flows generated by said swirl flowgenerating means are received.
 4. The combustion chamber structureaccording to claim 1, further comprising a swirl flow generating meansfor generating swirl flows within the combustion chamber, wherein saidcutaway portion is constructed by a groove formed in a direction inwhich the swirl flows generated by said swirl flow generating means arenot received.
 5. The combustion chamber structure according to claim 1,further comprising a tumble flow generating means for generating tumbleflows within the combustion chamber, wherein said cutaway portion isconstructed by a groove formed in a direction in which the tumble flowsgenerated by said tumble flow generating means are received.
 6. Thecombustion chamber structure according to claim 1, further comprising atumble flow generating means for generating tumble flows within thecombustion chamber, wherein said cutaway portion is constructed by agroove formed in a direction in which the tumble flows generated by saidtumble flow generating means, are not received.
 7. A combustion chamberstructure for an internal combustion engine comprising: a cylindericalhead having an inner wall surface and a cylinder block having an innerwall surface, wherein a combustion is defined by the inner wall surfaceof the cylinder head and the inner wall surface of the cylinder block,the combustion chamber having a top wall surface area with an intakeopening portion and an exhaust opening portion; a spark plug disposed incommunication with the combustion chamber; and a piston slidablypositioned within the combustion chamber, the piston including a topsurface having a circumferential edge with a projection, wherein theprojection has a surface that faces, and is substantially parallel with,the top wall surface area of the combustion chamber, wherein a cutawayportion if formed in the piston wholly within a portion of theprojection that faces an intake opening portion of the top wall surfacearea of the combustion chamber, and wherein the combustion chamber has alongitudinal cross-sectional shape that is generally pentagonal.
 8. Thecombustion chamber structure of claim 7, wherein the top wall surfacearea has a substantially triangular shape.
 9. The combustion chamberstructure of claim 7 wherein the spark plug is disposed adjacent the topwall surface area of the combustion chamber.
 10. The combustion chamberstructure of claim 7 wherein the spark plug is disposed at the top ofthe combustion chamber.
 11. A combustion chamber structure for aninternal combustion engine comprising: a cylindrical head having aninner wall surface and a cylinder block having an inner wall surface,wherein a combustion chamber is defined by the inner wall surface of thecylinder head and the inner wall surface of the cylinder block, thecombustion chamber having a top wall surface area with an intake openingportion and an exhaust portion; a spark plug disposed in communicationwith the combustion chamber; a swirl flow generator which introducesswirl flows into the combustion chamber; and a piston slidablypositioned within the combustion chamber, the piston including a topsurface having a circumferential edge with a projection, wherein theprojection has a surface that faces, and is substantially parallel with,the top wall surface area of the combustion chamber, wherein a cutawayportion is formed of the projection in the form of a groove formed in adirection in which swirl flows generated by the swirl flow generator arenot introduced into the cutaway portion.